Mobile communications technology has enjoyed substantial growth and advancement over the past decade. Such advancements have led to a widespread use of mobile stations that may be used in one or several cells by customers that frequently change position. When a terminating call attempt is placed to a mobile station (MS), the call is routed to the mobile station based on location information stored within a home location register (HLR). If the HLR is storing incorrect location information, the terminating call attempt is routed to an incorrect mobile services switching center (MSC). The incorrect routing causes the terminating call to not be received at the mobile station. The HLR may store incorrect location information when, for example, a location registration (LR) acknowledgment signal or a location erasure (LE) signal is not received by an MSC. Unsatisfactory link quality, congestion, signal loss, or a large amount of location erasures, among other things, may cause LE and LR acknowledgment signals to not be received by the MSC.
FIG. 2 illustrates the current LR signaling sequence, which cannot detect or correct erroneous location information at the HLR. A mobile station 10 first leaves an area controlled by a first MSC 30 and enters a new cell controlled by a second MSC 50. Upon entering the new cell, at step s200, the mobile station 10 makes a location registration request 21 with the second MSC 50. At step s202, the second MSC 50, in response to the LR request 21, makes a subscriber data request to the HLR 40. The subscriber data, in the HLR 40, associated with a particular mobile station 10 includes, among other things, the location information of that particular mobile station 10. The location information includes the identity of the MSC that controls the area in which the mobile station 10 is located. At step s204, the HLR 40 sends the subscriber data back to the second MSC 50. In response to receiving the subscriber data, at step s206, the second MSC 50 sends an authentication request to the mobile station 10 to confirm the identity of the mobile station 10. In return, the mobile station 10 transmits an authentication response to the second MSC 50 at step s208. At step s210, the second MSC 50 sends an LR to the HLR 40. The HLR 40, at step s212, sends an LR acknowledgment signal to the second MSC 50. If this signal is not received at the second MSC 50, then the LR attempt of the mobile station 10 fails and the second MSC 50 does not register the mobile station 10 in the second MSC 50 database. Assuming the second MSC 50 receives the LR acknowledgment signal, the second MSC 50, at step s214, sends the LR acknowledgment signal to the mobile station 10, which notifies the mobile station 10 that the LR is complete and successful.
When the LR acknowledgment signals are lost, the current solution is for the mobile station 10 to assume the location registration request failed and make a new location registration request every six seconds until the mobile station 10 receives the LR acknowledgment signal. After the HLR 40 sends the LR acknowledgment signal, at step s216, the HLR 40 sends a location erasure signal to the first MSC 30, which, for several reasons may not be received by the first MSC 30. To correct for the signal loss of an LE signal, the HLR 40 buffers and resends the LE signal up to five times, with up to thirty minutes between each attempt. When the first MSC 30 receives the LE signal, the subscriber data of the mobile station 10 associated with the LE signal is erased from the database of the first MSC 30. Once the subscriber data of the mobile station 10 is erased, at step s218, the first MSC 30 sends an LE acknowledgment signal to the HLR 40, which notifies the HLR 40 that the subscriber data of the mobile station 10 has been erased from the first MSC 30 database.
An example of an exemplary manner in which an HLR may store incorrect location information, with reference to the prior art technique shown in FIG. 1, begins with a mobile station 10 making a location registration request 20 to a first MSC 30. The HLR 40 updates the location information in the subscriber data associated with the mobile station 10 by replacing a previous MSC identity with the identity of the first MSC 30. The HLR 40 also sends a copy of the updated subscriber data to the first MSC 30. Then the mobile station 10 moves to a second cell controlled by a second MSC 50. Upon moving to the second cell, the mobile station 10 makes a location registration request 21 with the second MSC 50. The second MSC 50 informs the HLR 40 to update the subscriber data corresponding to the mobile station 10. The HLR 40 then replaces the location information, which indicates the identity of the first MSC 30 with the identity of the second MSC 50. The HLR 40 sends an LE signal to the first MSC 30, which, for example, due to unsatisfactory link quality, is not received. Therefore, the first MSC 30 does not remove the subscriber data associated with the mobile station 10. After the LE signal is lost, the mobile station 10 moves back to the first MSC 30. The mobile station 10 next makes a location registration request 22 with the first MSC 30. Because the first MSC 30 did not subtract the subscriber data associated with the mobile station 10, the first MSC 30 does not inform the HLR 40 that the mobile station 10 is now located in the area controlled by the first MSC 30. Consequently, the HLR 40 still has the identity of the second MSC 50 stored in the location information of the subscriber data for the mobile station 10. If the mobile station 10 now receives a terminating call attempt, the call is routed to the second MSC 50, which cannot contact the mobile station 10. Therefore, the terminating call attempt fails because the HLR 40 contains incorrect location information.
Despite the current solutions, some or all of the repetitive LE signals may be lost, which leads to the HLR containing incorrect information. Extenuating circumstances, such as a high number of erasures, cause the loss of all repetitive signals. The re-attempt buffer of the HLR has a size limit and may be congested, therefore causing all signals in excess of the limit to be lost. Also, by sending repeat LR requests from a mobile station, and executing the entire location registration procedure again, valuable time and capacity are consumed. A mobile station continues to make location registration re-attempts until successful, consequently allowing re-attempts to be sent several numbers of times. The central processor, air interface, and signaling links may get congested by sending an unlimited number of re-attempts. Therefore, there is a need to eliminate the invalid location information of mobile stations without congesting the system as in the current state-of-the-art.